As in Meek, surpluses can be transferred in any round, and you don't need to know how a ballot
counted in a previous round to know how it will count in the current round. However, it
adopts Warren's use of maxima instead of a surplus fraction, so ballots are split into smaller
pieces, and each voter is associated with a smaller number representatives. IRSA counts more
votes for winners by recasting exhausted ballots that are still countable. By keeping ballot
fractions as large as possible, IRSA is plausibly hand-countable.
Read the
IRSA specification
and arguments for it, or a
slideshow featuring IRSA.